["Corporate Social Responsibility and Environmental Management, Volume 33, Issue 2, Page 2384-2412, March 2026. ", "\nABSTRACT\nThis study examines the conditional relationship between corruption and sustainable firm growth (SFG) through the lens of financial inclusion, offering new insights into how institutional quality moderates the effects of corruption on firm‐level outcomes. Drawing on panel data from 465 non‐financial firms across nine MENA countries between 2007 and 2020, we apply a Dynamic Panel Threshold Regression (DPTR) model to assess whether financial inclusion acts as a threshold mechanism that transforms the corruption–growth nexus. The results reveal a statistically significant financial inclusion threshold at 0.250 (25%), below which CPI (low corruption) exerts a negative effect on SFG, supporting the “grease in the wheels” hypothesis. Above this threshold, the effect turns positive, aligning with the “sand in the wheels” theory. These findings suggest that financial inclusion does not simply mitigate corruption; rather, it reconfigures the institutional environment, shifting corruption from a compensatory mechanism to a systemic constraint. Our results are robust to alternative measures of growth and estimation techniques. Theoretically, we contribute to institutional theory by introducing a non‐linear, threshold‐based framework that contextualizes corruption's role in firm performance. Empirically, we offer novel evidence from a region characterized by institutional volatility, highlighting how financial infrastructure can condition firm behavior. For policymakers, the findings underscore the strategic importance of inclusive financial systems in reducing firms' reliance on informal practices and fostering more transparent, sustainable growth.\n"]